The purpose of the proposed research is to develop a method of using cultured thymic epithelium in various types of immunodeficiency. In so doing, it is our intent to come to a greater understanding of mechanisms of thymic differentiation as well as define the clinical conditions which might benifit from this therapy. The ability to improve the immunity of various patients will also provide greater insight into the nature of thymic influence in mechanisms of immunity. In vtro and in vivo studies will be performed. In vitro, cultured thymic epithelium will be used with various lymphoid cell proparations and the degree of T and B cell differentiation measured by using cell surface markers and varios in vitro responses characteristic of differentiated T and B cells. The morphology of interaction will be studied. In vivo, restitution of nude mice, neonatally tymectomized mice and genetic deficiencies of man will be attempted. Analysis of tests of competent T and B cell function, morphological studies of lymphoid tissue and clinical improvement will be accomplished.